There are a broad range of situations in which feed materials must be processed in manners resulting in their milling or grinding (terms used herein interchangeably), mixing, blending, separation, drying and sterilisation. For example, many production processes require the use of ground, mixed, blended, dried or sterilised ingredient materials and indeed in recent times it has been recognised that physical characteristics of materials may be advantageous or may in fact alter once the materials are processed to a micro- or nano-particulate diameter. For example solubility, emulsification, colloid forming, light defraction or reflection and absorption properties of materials may be advantageous if the materials are processed to a fine particulate form. For example, the use of a fine particulate form of zinc oxide allows the preparation of transparent zinc oxide containing sun protection creams and fine particulate forms of pharmaceutical agents may exhibit modified pharmacokinetic characteristics such as allowing dermal penetration or more rapid absorption across the gastrointestinal tract.
It is also a focus in this era of increasing environmental concern to minimise the negative environmental impact of industrial and agricultural processes and it has now been demonstrated that processing of feed materials by milling, mixing, blending, separating, drying and sterilisation may provide opportunities to produce useful products or materials from waste materials that would otherwise have been discarded, burned or buried with the potential for a negative environmental impact. Adoption of processes such as these that result in what otherwise would be considered as waste materials having some economic value are likely to encourage commercial entities to be more responsible with their waste materials.
Not only may milling, mixing, blending, separation, drying and sterilisation processes be of potential utility in waste management and production of fine particulate materials, but such processes may also be useful in the production of powdered foodstuffs, food ingredients or nutritional supplements, production of cosmetics, toiletries and pharmaceuticals, recycling of various materials, paint and dye-stuff manufacture, mineral refining and a broad range of other applications.
Commonly, processes for grinding or milling materials will also produce other process outcomes such as drying and separation, and if more than one feed material is involved, additional outcomes such as mixing and blending may result.
A known form of processing by grinding involves use of a high velocity fluid, particularly air, in a fluid jet pulverising mill (which may also be known as a fluid energy mill) or an anvil mill, wherein particles of a feed material are typically entrained in a vortex of the airstream within a grinding chamber. Highly pressurised air is supplied into the grinding chamber so as to form the vortex and the grinding of particles of feed material is effected by the action of the airstream on the particles and by abrasive contact of the particles with one another and with the sides of the grinding chamber or anvils disposed therein.
In fluid energy or jet mills the autogenous pulverisation of particles is driven by the supplied highly pressurised (that is, compressed) gas or air, and such mills are thus distinguished from hammer mills in which the pulverisation occurs by means of high speed rotating pulverising elements or hammers. Thus fluid energy mills, in contrast to hammer mills, do not include any moving parts. They do, however, involve significantly higher operating expense than hammer mills as the supply of compressed air or gas is a highly expensive medium for supply of energy. Fluid energy mills are also characterised by high capital costs associated with, for example, the required gas compressors, as well as high running and maintenance costs and a relatively low efficiency of utilisation of the compressed gas to effect pulverisation. Known fluid energy mills are typically in the range of ten times more expensive than hammer mills with respect to the cost of ground product. Consequently the milling of only high value specialty products can justify the costs of utilising a fluid energy mill. The milling in fluid energy mills of commodity products such as coal, cement, minerals, building materials, recycled materials, biomass or waste from food manufacture or other industrial processes generally cannot be conducted at an economically viable cost.
An example of a fluid milling apparatus is disclosed in international patent publication WO 00/56460 that relates to a device comprising an upper annular chamber into which feed material is introduced, and a lower conical chamber. A high velocity vortex flow of compressed air is introduced into the chamber, which gives rise to milling and drying of a feed material.
The present inventors have now devised a processing apparatus and methods for processing feed materials that may offer certain advantages relative to earlier apparatus and methods, such as reduced capital and operating costs and increased processing efficiency.